In recent years, laser marking has become widely used as a method of specifying the date of manufacture, use-by date, name of the manufacturer, product name, and serial number and the like on the surface of beverage cans, beverage containers, cosmetics containers and pharmaceutical containers, or electronic components, electrical components, electrical products, vehicle components, sheets and cards and the like. Laser marking methods are non-contact, offer rapid marking, are capable of marking materials regardless of their surface shape, and can be readily automated and controlled. In addition, laser marking enables direct marking of the material itself, meaning marking can be completed without the use of typical solvent-containing inks, and as a result, laser marking has recently been attracting considerable attention as an environmentally clean marking method.
In the case of printed matter generated by conventional laser marking (for example, see Japanese Patent Laid-Open No. H05-229256, Japanese Patent Laid-Open No. H05-254252, Japanese Patent Laid-Open No. H05-301458, Japanese Patent Laid-Open No. H08-25809, Japanese Patent Laid-Open No. H10-138642, Japanese Translation of PCT International Application No. 2004-522631, and Japanese Patent Laid-Open No. H03-270980), in addition to issues relating to the sharpness and contrast of the printing, in most cases the printed matter comprises either black or brown printing on a white background or white printing on a black background, meaning the printed matter lacks color tone.
Furthermore, conventional laser marking methods are generally only capable of printing onto a surface, and for example, no technology exists for simultaneously forming convex protrusions in addition to the printing, thereby embellishing the printing in terms of both feel and visual appearance. In contrast, the convex protrusion forming capabilities of foaming inks are widely used for a variety of applications including Braille printing, weight reduction, preventing bottle breakage, delustering, surface modification processing, heat insulation and cushioning, but coloring only the foamed portions a different color from the foaming ink layer is generally impossible. Accordingly, depending on the way in which the printed matter is used, the existence or location of the convex protrusions can be difficult to detect.